Focus-detector arrangements for generating projective or tomographic phase contrast recordings of a subject are generally known. By way of example, reference is made to the European patent application EP 1 447 046 A1 and the German patent applications (not yet published that the priority date of the present application) with the file references 10 2006 017 290.6, 10 2006 015 358.8, 10 2006 017 291.4, 10 2006 015 356.1 and 10 2006 015 355.3.
For imaging by ionizing rays, in particular X-rays, essentially two effects can be observed which occur when the radiation passes through matter, namely absorption and the phase shift of the radiation passing through a subject. It is also known that in many cases, the phase shift when a ray passes through a subject depends much more strongly on small differences with respect to the thickness and composition of the penetrated matter than the absorption does. This allows structures of a subject, in particular the soft structures of a patient, to be recognized better.
For such phase contrast radiography or phase contrast tomography, the phase shift of radiation due to the object must be evaluated. Here, similarly as conventional absorption contrast X-radiography or absorption contrast X-ray tomography, both projective images of the phase shift can be compiled and tomographic representations of the phase shift can be calculated from a multiplicity of projective images.
Such phase shifts can be determined by using interferometric gratings and used for generating projective or tomographic recordings. In respect of these interferometric measurement methods, reference is made to the documents cited above. In these methods, coherent or quasi-coherent X-radiation is passed through a subject, then delivered through a grating with a period matched to the wavelengths of the radiation so that beam splitting takes place first and superposition of the split beams leads to an interference pattern which is modulated by the phase shift due to the object. This interference pattern is measured by a subsequent analysis-detector arrangement, so that the phase shift can be determined. A phase grating is preferably used as the beam splitter.
It is also known to produce such phase gratings, as well as the basic structures of the analyzer gratings, for example by etching rectangular structures from a silicon wafer. A problem with such rigid gratings made of silicon wafers, e.g. phase gratings as beam splitter gratings, amplitude/absorber gratings as analyzer gratings or source gratings, is for example that the accuracy of the structures which can be produced with tolerable outlay is sometimes insufficient. Furthermore, the extent of such silicon wafers is limited by the size of the basic material. Assembling a plurality of sub-pieces can lead to artifacts during the measurement. A further problem is that adaptation to different radiation energies and adaptation of the period and the Talbot distance of the interference pattern is possible only by replacing the relevant gratings.